The present invention relates to a seat belt retractor for withdrawing and retracting a seat belt, and more particularly, to a bearing for a reel for retracting a seat belt.
A conventional seat belt device provided in a vehicle, such as an automobile, restricts movement of a passenger when an emergency occurs, for example, when the vehicle is affected by a large deceleration caused by a crash or the like. The seat belt device prevents the passenger from moving away from the seat, thus protecting the passenger.
This seat belt device includes a seat belt retractor for allowing the seat belt to withdraw and retract. The seat belt retractor has urging means, such as a helical spring, for urging a reel for retracting the seat belt constantly in a retracting direction. The force of the urging means retracts the seat belt on the reel when the seat belt is not fastened. When a passenger fastens the seat belt, the seat belt is withdrawn against the force of the urging means. When the emergency occurs, a lock mechanism of the seat belt retractor is actuated to prevent the reel from rotating in a withdrawing direction. The seat belt is thus stopped from withdrawal. This reliably restricts the movement of the passenger when the emergency occurs, thus protecting the passenger.
In this seat belt retractor of the conventional seat belt device, the reel for retracting the seat belt has a rotary shaft. An end for receiving the force of the urging means, which acts in the belt retracting direction, is rotationally supported by a side wall of the retractor""s U-shaped frame. The other end of the rotary shaft at which the lock mechanism is provided is rotationally supported by a cover of the lock mechanism. In this case, as shown in FIG. 10, an end c of a rotary shaft b, which is supported by a lock mechanism cover a, is rotationally supported at the periphery of the end c by a cylindrical bearing d formed in the cover a.
In this structure, in which the rotary shaft end c is rotationally supported by the bearing d at the outer circumference of the end c, a bearing hole e is formed in the lock mechanism cover a for supporting the rotary shaft b. A clearance is formed between the circumferential wall of the bearing hole e and the periphery of the end c of the rotary shaft b. This causes the shaft b to become radially unstable. Accordingly, in the conventional device, a cylindrical projection g projects axially from the middle of a bottom of the bearing hole e, which is formed in the cover a. Further, an annular hole h is formed in the middle of the associated surface of the rotary shaft b. The projection g is fitted in the annular hole h to allow the rotary shaft b to rotate. This supports the end c of the rotary shaft b to stabilize the shaft b in the radial direction.
However, the radial stabilization of the rotary shaft with this bearing support structure is still inefficient and insufficient. That is, the rotary shaft is radially stabilized only in a limited manner. Further, as another method for stabilizing a rotary shaft, a method in which a shaft end is urged toward a bearing of a cover with a decreased force has been employed. However, the stabilization of the rotary shaft by this method is also insufficient.
Accordingly, the present invention has been made to solve the above problem, and it is an object of the present invention to provide a seat belt retractor that stabilizes a rotary shaft in the radial direction and suppresses rotational resistance.
To achieve the above object, in the first aspect of the invention, a seat belt retractor includes at least a reel for retracting a seat belt, a rotary shaft for the reel, and a bearing for rotationally supporting an end of the rotary shaft. In the seat belt retractor, a rotary shaft end support having an opposing surface opposing the end of the rotary shaft and supporting the end of the rotary shaft is provided in the bearing, and the end of the rotary shaft is formed as a curved surface with the opposing surface of the bearing formed as a curved surface shaped identical or substantially identical to that of the end of the rotary shaft.
In a second aspect of the invention, the curved surface is a spherical surface or a conical surface.
In a third aspect of the invention, the rotary shaft end support is provided along a predetermined area extending in a circumferential direction of the end of the rotary shaft.
In a fourth aspect of the invention, the rotary shaft end support is divided into a predetermined number of sections in the circumferential direction of the end of the rotary shaft.
In a fifth aspect of the invention, the divided sections of the rotary shaft end support are arranged at equal intervals in the circumferential direction of the rotary shaft.
In the seat belt retractor according to the present invention, the rotary shaft end is rotationally supported by the bearing such that the curved end surface of the rotary shaft abuts against the curved opposing surface of the rotary shaft end support in a matched manner. The rotary shaft is thus supported by the bearing to rotate both in the radial and axial directions. Accordingly, the rotary shaft is stabilized efficiently and sufficiently at least in the radial direction.
Particularly, in the invention described in the third aspect, the rotary shaft end support is provided along a predetermined area extending in a circumferential direction of the end of the rotary shaft. This reduces the rotational resistance when the rotary shaft is rotated.
Further, in the invention described in the fifth aspect, the predetermined number of sections of the rotary shaft end support are arranged at equal intervals in the circumferential direction of the end of the rotary shaft. That is, these sections of the rotary shaft end support are located separately from one another with respect to the entire circumference of the rotary shaft end. Accordingly, the rotational resistance of the rotary shaft end support acts uniformly on the rotary shaft, thus enabling the rotary shaft to rotate smoothly. This suppresses unstable rotation of the rotary shaft.